M42 Threads

[John Parry]

Hi Everyone,

Seeing the Soligor lens in "A Spotmatic Package Deal"
reminded me of a couple that I own - a 400 and a 300.
But they have developed a problem that you're going
to find hard to believe (no it isn't April 1st). The threads
have changed on the M42 mounts. Both lenses used to
screw into my Praktica MTL5B and MTL50 with no
problems at all. Now they don't - simple as.

Both will screw in a couple of turns, then lock solid. Aha -
crossed threads, I hear you cry. Nope - I had the threads
filed out by a mechanical engineer friend, and he is
prepared to swear that they aren't crossed. They just
don't fit the M42 bodies.

One more aspect to the mystery, both lenses will screw
without problems into a Vivitar 2x extender that I have
- as will all my other M42 lenses!

I mentioned this on the Praktica User Group site, but
nobody there had a clue what was happening. I know
there are different pitches of M42, but I keep coming
back to "Why would it change". Any thoughts anyone?

Regards - John

[PeterW]

Hi John,

This is the second try at posting this, the first just disappeared, so let's hope this gets through OK.

I have come across this problem before, and in those cases it was because the lens thread was T-mount. The so called universal M42 camera thread is M42 x 1.0mm pitch. The most usual T-mount thread is M42 x 0.75mm. There is a T-2 mount thread of M42 x 0.38mm but fortunately this is relatively rare.

Point is that the specifications for M42 threads allow for different classes of fit, and on cameras it's usually classed as a 'medium' fit and the full specification is M42 x 1.0 -6 (the higher the -X number the looser the fit).

When an M42 x 1.0 female and M42 x 0.75 male thread are both unworn it's not uncommon to find that they seem to marry. But after a time the mis-match wears the flanks and they bind. The first signs are often that the lens feels 'jerky' as it screws in.

On one example I found the lens was screwed into the camera but would unscrew only a couple of turns before going solid. The only way to get it out was by alternately pushing in and pulling out and even then it was tight. It's possible that the lenses screw into your Vivitar adaptor OK because the Vivitar threads are unworn.

Have you by any chance got a T-mount adaptor you can try them in? You used to be able to buy T-mount to M42 x 1.0 adaptors in most camera shops, but I haven't seen them around for a while.

If this isn't the cause of your problem, then I'm stumped.

Peter

[John Parry]

Hi Peter,

At last - someone who believes it can happen! Thanks for that info. Just did an open search for Soligor on Google, and it appears that they (along with Paragon) pioneered the t-mount. So it's quite possible that somebody sold me the lenses unwittingly. (In fact I think one was bundled with a Praktica I bought).

Now that I know what to look for I'm sure I'll find an adapter somewhere.

Regards - John

[herron]

Peter:
I think you're right about the different thread pitch, and the fact that wear seems to aggravate the difference. I first noticed it many years ago in some thread-mount Super Takumar lenses that jammed in a Mamiya mount after about a year of using them (very difficult to remove, too).

Frustrating, when it happens. The different thread pitch is not something you can easily see.

[PeterW]

The different thread pitch is not something you can easily see.

You're right there. Ron. On the lens there's usually only 3 to 4 pitches, and it's very difficult to try to measure the pitch with a thread gauge. The only accurate way to do it is with an optical projector to throw the thread profile up on a screen about 10x actual size. But these are very expensive and found only in the big optical labs.

Peter

[John Parry]

Absolutely spot on Peter.

Bought a lens on eBay, which had an adapter on it. I would't have noticed except that it was loose. It fitted my M42's perfectly, and the two 'faulty' lenses I had. So I put in a 'buy it now' for a fiver for a Praktica bayonet T2 mount adapter. Can now use all my lenses on all my Prakticas and the Fuji ST605 (which I really like very much indeed btw).

A happy ending!

Regards - John

[aceroadholder]

Peter, many well equiped machine shops have shadow projectors. It would only take several minutes for them to measure a thread for you. Probably would do it gratis if you made a nice photo of the owners premises!

Orlin in SC/USA

[kamera]

Ah ha!

That would also probably explain what happened when once I thought I screwed an M42 on so tight it stripped, which a couple people told me is impossible.

And up till now I have been taking any 'new' 42(oo, oo...that rhymes) to Mother Paula, the local psychic/medium for a blessing before putting them on a camera... ;D ;D...!

Ron Head
Kalamazoo, MI

[PeterW]

Hi Bud,

Sorry, you've lost me ... or I've lost you . What site are we talking about?

Peter is the site Oracal...

Peter

[John Parry]

Nice to see you back on here Bud - quite an explosion of posts!

Regards - John

[John Parry]

Peter

He means Ocelot !!

John